Terpinolene, or para-mentha-1,4(8)-diene, is a terpenoid hydrocarbon. It has a sweet-piney, oily and relatively pleasant odor. It is used as a fragrance providing ingredient for household cleansers, in deodorizers, "reodorants", masking agents, etc. It is also useful as a starting material for the preparation of terpineol, or 1-methyl-4-isopropylidene cyclohexanol-1. It is also used as a chain terminating agent in certain aqueous polymerizations. Industrial demand has increased giving rise to a need for a more efficient process for producing terpinolene and minimizing the production of concomitant by-products.
Catalytic isomerization of (+)-transisolimonene to optically active (+)-isoterpinolene has been carried out using high surface sodium on alumina which has been partially deactivated. Partial deactivation limits the production of p-cymene, an undesired product of lesser value. (See Indian Pat. No. 146,086 filed June 26, 1976).
Metatitanic acid has been used as a catalyst in the isomerization of 2-carane oxide to cis-isolimonenol (See U.S. Pat. No. 3,814,733 to Bledsoe et al. It has also been used to isomerize dipentene and terpinolene although yields of terpinolene from dipentene were low (21%) and not as high as with ohydroxy benzoic acid catalyst (Chem. Abst. 81(13)78097d).
It has now been found that orthotitanic acid is an effective catalyst in terms of selectivity and conversion for the selective isomerization of limonene to terpinolene provided the reaction is carried out in the presence of a small amount of an alkali metal alkaline earth metal or ammonium salt of a weak acid as a buffer, e.g., sodium acetate.